Fraser Valley Conservancy officials were ready to stop vehicle traffic in Ryder Lake to make way for the annual western toad migration.
But for some reason very few toadlets ended up crossing the road this year.
Conservancy reps are now talking about a possible crash in population numbers of the blue-listed toad species.
"The toads have been a bit of a mystery this year," said biologist Micheal Pearson, president of the FVC.
The totals are just "a small fraction" of previous years' numbers.
"We think the migration is almost over," he reported in a news release.
The juvenile toads typically follow a migration route from their natal lakes up in the Ryder Lake area to nearby forested rearing grounds across the road. They are numbered in the tens of thousands, with a visual count of 700,000 last year.
This year there were only about 20,000 toadlets, based on a rough estimate by the Conservancy.
There weren't enough juveniles on the move to justify closing the roads for extended periods.
"We are not sure what has happened, as the adults seemed to show up in the usual numbers to breed this spring," said Pearson.
They've heard reports of a similar crash in a population on Vancouver Island — also unexplained.
"It may be a disease outbreak, but at the moment we simply don’t know. It is also unlikely we ever will for sure."
Confirmation would have to come from "not quite dead" specimens, which they do not have at the moment.
One of the obstacles is gaining access to the breeding and rearing sites.
"It is difficult as both water bodies (Ryder Lake and Hornby Lake) are on private land," said Pearson.
They obtained swab samples from two toads to test for Chytrid fungus, which has caused amphibian crashes elsewhere.
"But even finding it will not be conclusive, as it commonly occurs at low levels without causing harm.
"At present we are still monitoring the situation and discussing possibilities with some BC amphibian specialists," said Pearson.
The FVC will continuing its efforts to raise funds for crossing structures for its Western Toad Migration program.
"I think this shows how important it is to make sure the adults can migrate safely to breed to keep their populations healthy, especially when they have one bad year," said FVC official Suzie MacMillan.
The road closure signs are coming down this week, she added.
jfeinberg@theprogress.com
twitter.com/CHWKjourno